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Q11. A and B together can complete a particular task in 4 days. If A alone can complete the same task in 12 days. How many days will B take to complete the task if he works alone
(A) 6 days
(B) 7 days
(C) 8 days
(D) 5 days
Answer: 6 days
Explanation: If A and B together can do a piece of work in x day and A alone can do it in y days, then B alone can do the work in ( xy / y-x ) days. Given A and B together finish a piece of work = x = 4 days. A alone finish a piece of work = y = 12 days. By the short trick approach: B alone can do the whole work in ( 4 x 12)/(12-4 ) = 48/8 = 6 days
Q12. A and B together can finish a work in 9 days. A alone can finish the work in 12 days. In how many days will B alone finish the work?
(A) 48 days
(B) 24 days
(C) 18 days
(D) 36 days
Answer: 36 days
Explanation: If A and B together can do a piece of work in x day and A alone can do it in y days, then B alone can do the work in ( xy / y-x ) days. Given A and B together finish a piece of work = x = 9 days A alone finish a piece of work = y = 12 days. By the short trick approach: B alone can do the whole work in (12 x 9)/(12-9 ) = 108/3 = 36 days
Q13. A man can row 15 km downstream in 3 hours and the same distance upstream in 5 hours. Find the speed of the stream
(A) 2 km/h
(B) 1 km/h
(C) 1.5 km/h
(D) 2.5 km/h
Answer: 1 km/h
Explanation: . Speed of stream = ( 15/3-15/5 ) / 2 = (5-3 ) / 2 = 1 km/h
Q14. The ratio of the number of boys to girls in a class is 7:5 . If there are 35 boys, how many girls are there
(A) 20
(B) 35
(C) 30
(D) 25
Answer: 25
Explanation:Number of girls = 35 × (5/7 ) = 25
Q15. A person buys an item at Rs. 240 and sells it at a loss of 20 %. What is the selling price
(A) Rs. 192
(B) Rs. 172
(C) Rs. 202
(D) Rs. 182
Answer: Rs. 192
Explanation: Selling price = 240 × 0.80 = Rs. 192